Automobile air bags systems are recognized as the best means to prevent trauma in an automobile accident. Designed to deploy when a vehicle travelling at velocities of 12 m.p.h. or greater experiences a sudden impact, the air bag inflates with a non-toxic gas to form a soft barrier, preventing occupant impact with the automobile interior or windshield. Thus, serious injuries are averted.
Air bags systems have been disclosed in patents as early as the 1950's. By the 1970's such systems were included in Ford, General Motors and Volvo automobiles. Passengers of those vehicles who became involved in accidents were spared serious injury by deployment of the system, conclusively proving the system's beneficence.
The typical air bag system is generally comprised of a sensor that sets off an explosive train, in which the last component is a gas generating device. The gas generating device contains a gas generating composition (a/k/a inflator). The sensor, which operates on mechanical or electro-mechanical principles, senses the energy generated by the crash. Energy is transferred to the sensor starts the explosion train. The gas generating composition rapidly inflates the bag with a non-toxic gas.
The two important components of the airbag system are the sensing device and the gas generating composition. The sensing device, which picks up the energy of the automobile crash and sets off the explosive train, can be either an electromechanical device with a diagnostic system or a mechanical device. A variety of gas generating compositions have been developed to fill the airbag. One of the earliest was that developed by Dow Chemical based on Oxamide as fuel and potassium perchlorate as the oxidizer, along with a coolant, which generated a gas containing 85% carbon dioxide and 13% nitrogen (Proceedings of 3rd International Pyrotechnics Seminar, Denver Res. Institute, Colorado 1972). A number of patents disclose the gas generating compositions, where the non-toxic gas filling the airbag is carbon dioxide. See e.g., U.S. Pat. Nos. 3,532,357, 3,647,353, 3,964,255 and 3,971,729. However, utilizing carbon-dioxide as the airbag-filling gas has not been accepted by the automobile industry, probably due to the fact that incipient oxidation may result in formation of carbon-monoxide, potentially a health hazard at 400 ppm levels. Hence, most of the development has been based on the use of metallic azides in combination with an oxidizer, where the gas generated to fill the airbag is nitrogen. There are numerous patents covering the use of metallic azides for gas generating compositions:
U.S. Pat. No. 3,741,585 discloses the use of metallic azides with metallic sulfides, iodides, oxides and sulfur to generate low temperature nitrogen gas generating composition.
U.S. Pat. No. 3,936,300 discloses the use of sodium azide as the fuel and potassium chlorate as the oxidizer, along with other additives, for the gas generating composition in airbags.
U.S. Pat. No. 3,947,300 discloses the use of sodium azide as the fuel, potassium nitrate as the oxidizer, along with silicon dioxide for slagging out the product of reaction for gas generating composition to be used in airbags. The preferred proportion in which the fuel, oxidizer and slagging agent are to be used are 5:1:2 to 10:1:5. The other oxidizers mentioned in the patent are sodium nitrate, magnesium nitrate, calcium nitrate, sodium perchlorate and potassium perchlorate and the other fuels mentioned are potassium azide and calcium azide.
U.S. Pat. No. 4,547,235 discloses the use of sodium azide in combination with potassium nitrate (an oxidizer) along with silicon dioxide, molybdenum sulfide and sulfur for the gas generating composition in airbags.
U.S. Pat. No. 4,604,151 discloses the use of an alkali metal azide, along with a mixture of metal oxides including manganese dioxide, iron oxide and nickel oxide. The combination of the metal oxides and ammonium perchlorate generate nitrogen gas for airbags.
U.S. Pat. No. 4,696,705 discloses the use of sodium azide in combination with iron oxide, sodium nitrate (as an oxidizer), bentonite, fumed silica, and graphite fibers to generate nitrogen gas to inflate airbags.
U.S. Pat. No. 4,734,141 discloses the use of sodium azide and an oxidizer consisting of bimetallic complexes containing copper or iron in combination with chromium, molybdenum or tungsten and a lubricant like magnesium stearate for generating non-toxic nitrogen gas for the airbags.
U.S. Pat. No. 4,806,180 discloses a gas generating composition for use in airbags consisting of a metal azide (30-50%) sodium nitrate or potassium perchlorate (40-60%) along with Boron 5-15%) and sodium silicate (1-15%).